Yusuf al-Mu'taman ibn Hud

Yusuf al-Mu'taman ibn Hud, also known as al-Mu'tamin, was the ruler of the Taifa of Zaragoza in Reconquista-era Spain from 1081 to 1085, succeeding Ahmad al-Muqtadir and preceding al-Mustain II.

Islamic scholar
Yusuf al-Mu'taman ibn Hud was born to a Sunni Muslim family of Moors in the city of Zaragoza in northern Spain, ruling the city from 1081 to 1085. An accomplished polymath in the fields of mathematics, medicine, philosophy, and astronomy, he inherited these skills from his father Ahmad al-Muqtadir, and he translated Greek and Roman texts into Arabic and Andalusian. He offered copious and revolutionary ideas on Greco-Roman insight, and he proved Ceva's theorem on parallel lines in triangles hundreds of years before Giovanni Ceva even coined the term.

Emir of Zaragoza
Yusuf was captured by the Christian Spanish nobleman Rodrigo Diaz de Vivar in battle alongside Emir al-Kadir of Valencia after burning down a town, and al-Mu'taman warned the cruel Garcia Ordonez that his sons would fight until all Christians in Spain were dead if he was to be hanged in Burgos as ordered by King Sancho II of Castile. However, Rodrigo refused to have the emirs executed, releasing them after they swore to not attack Castile again. They nicknamed him "El Cid", meaning "the lord", and they swore allegiance to him. Yusuf saved El Cid from an assassination attempt by his betrothed wife Ximena (who was angry at El Cid's killing of her father Count Gormaz in a duel), and he helped his lord in taking Zaragoza and defending it from Ibn Yusuf's army in 1099. When El Cid was killed in battle, Yusuf rode alongside El Cid's horse Babieca on his own steed as Babieca - with El Cid's body strapped to it - charged the enemy lines and tramped Ibn Yusuf and several frightened Moors, a final act of respect for his old master.